A Democrat and longtime local lawmaker, Trotter faces charges for attempting to bring a weapon onto a plane at O'Hare International Airport in early December. He told law enforcement officials he forgot the gun was in his bag. He is scheduled to appear in court in January to contest the charges.

Trotter leaves a crowded and complicated primary for the 2nd District, which includes the south side of Chicago, southwestern suburbs and some rural territory west of the stateline. It's a heavily Democratic district, and the winner of the Feb. 26 primary is expected to be the next member of Congress.

There are at least six, well-known local Democrats in the race: Alderman Anthony Beale, former Rep. Debbie Halvorson, former NFL linebacker Napoleon Harris, state Sen. Toi Hutchinson, Cook County Chief Administrative Officer Robin Kelly and former Rep. Mel Reynolds.

Initially, Democrats viewed Trotter as a frontrunner to win the party's endorsement in the slating on Dec. 15. But local party officials were unable to reach a consensus about a candidate when they met.